# Multiphoton Effects Enhanced Due to Ultrafast Photon-Number Fluctuations

## TL;DR

This paper demonstrates that ultrafast photon-number fluctuations in bright squeezed vacuum significantly enhance multi-photon optical harmonic generation, offering a more efficient approach for nonlinear optics applications involving fragile structures.

## Contribution

The study introduces the use of bright squeezed vacuum with quantum noise as a pump to greatly enhance multi-photon effects, surpassing traditional coherent sources.

## Key findings

- Up to two orders of magnitude increase in harmonic generation efficiency.
- Ultrafast photon-number fluctuations boost multi-photon effects without increasing damage risk.
- Potential applications in nonlinear optics of fragile structures.

## Abstract

Multi-photon processes are the essence of nonlinear optics. Optical harmonics generation and multi-photon absorption, ionization, polymerization or spectroscopy are widely used in practical applications. Generally, the rate of an n-photon effect scales as the n-th order autocorrelation function of the incident light, which is high for light with strong photon-number fluctuations. Therefore `noisy' light sources are much more efficient for multi-photon effects than coherent sources with the same mean power, pulse duration and repetition rate. Here we generate optical harmonics of order 2-4 from bright squeezed vacuum (BSV), a state of light consisting of only quantum noise with no coherent component. We observe up to two orders of magnitude enhancement in the generation of optical harmonics due to ultrafast photon-number fluctuations. This feature is especially important for the nonlinear optics of fragile structures where the use of a `noisy' pump can considerably increase the effect without overcoming the damage threshold.